High voltage (HV) circuits are often used in vehicles such as hybrid electric vehicles (HEVs) and Battery-Electric Vehicles (BEVs) to provide power to HV components such as electric machines. For safety reasons, HV circuits are required to be both insulated and isolated. Insulation prevents direct contact with the HV circuit while isolation prevents the HV circuit contacting low voltage circuits in the vehicle that often use the body of the vehicle as ground. There is, therefore, a two stage safety system to make safe the use of HV circuits. Loss of isolation represents a risk to vehicle occupants and bystanders because components outside of the insulated HV circuit may become part of the HV circuit and may be contacted by the occupants of and bystanders to the vehicle. Therefore, upon detection of the loss of HV isolation, a controller usually instructs shutdown of the HV circuit, which may be performed immediately or, if the vehicle is moving, may be performed as soon as the vehicle comes to a standstill.
Vehicles having HV circuits may often come into contact with water. During water contact, the HV circuits and HV components might themselves come into contact with or be surrounded by water. Water contacting the HV circuit or components would not necessarily damage the HV circuits or components in the sense of damaging the insulation but could, for example, surround the circuit or components such that an electrical connection is formed between the HV circuit and, for example, the body of the vehicle via the water, therefore removing the isolation of the HV circuit.
Off-road vehicles are able to wade to a threshold depth that is often much higher than the height at which the HV circuits are positioned in the vehicle. HV circuits, albeit insulated, may therefore be submerged in water. Where connections are formed in the circuit, for example at contact terminals of an electric machine, water may cause a reduction or total loss of isolation and so HV circuits are usually shut down for the reasons discussed above.
After contact with water, the cause of the HV circuit isolation loss may be removed because the electrical path through the water is removed. However, by this time, shutdown of the HV circuits has usually been performed or at least initiated. This means that vehicles capable of wading, and other vehicles which may come into contact with water, may be rendered partially or wholly unusable by temporary water contact.
It is against this background that the present invention has been conceived.